Modern fuel-injected, fuel delivery systems are currently in use for supplying fuel to marine internal combustion engines because fuel injection precisely regulates fuel flow enabling accurate control of the air and fuel mixture entering the engine. This improves engine performance, particularly over the wide range of operating loads and conditions typically encountered by a marine engine providing better fuel efficiency while significantly reducing undesirable exhaust gas emissions.
During operation of a typical fuel handling system for a non-marine, fuel-injected, internal combustion engine, an electrically powered, high pressure fuel pump transfers liquid fuel from a remote tank, along a fuel line, into a fuel rail that communicates the fuel to individual fuel injectors of the engine. During engine operation, fuel not consumed by the engine is returned to the remote tank while unburned fuel vapor is typically remixed with air entering the engine or the fuel vapor is returned to a vapor storage container until it can be later remixed with engine intake air.
For the marine industry, exhaust gas emission regulations and the likely future trend of these regulations have made it highly desirable, and even virtually necessary, for engineers and designers to apply fuel injection systems to marine internal combustion engines used to power boats and other watercraft. However, because fuel handling for fuel injected fuel delivery systems requires fuel to be supplied to the engine at a high pressure of typically at least twenty pounds per square inch (PSI) or more, Coast Guard safety regulations designed to prevent marine engine and fuel handling system related fires and explosions have made use of fuel-injection technology for marine applications a challenge.
To comply with these Coast Guard safety regulations, which limit the length of pressurized fuel lines in marine fuel handling systems to no more than twelve inches, fuel is delivered by the high pressure fuel pump to the injectors from a fuel reservoir, referred to as a vapor separator, located close to the engine. A lower pressure fuel pump transfers fuel, as it is needed, from the remote fuel tank to the vapor separator so the high pressure pump always has an adequate supply of liquid fuel to deliver to the engine. Typically, to keep the length of the pressurized fuel line as short as possible, the high pressure fuel pump, vapor separator and pressurized fuel line are all carried by the engine and housed under its cowling.
Since it is impractical and possibly unsafe to return unused fuel to the remote fuel tank and because excess pressurized fuel not used by the injectors must also have a short return line preferably to conform to these same Coast Guard safety regulations, the reservoir also functions as a vapor separator. To perform as a vapor separator, the reservoir has a gas dome above a pool of liquid fuel in the reservoir. During operation, unused fuel and vapor is typically returned from the engine to the reservoir and vapor vented from the gas dome is mixed with air entering the engine to be burned during engine operation. An example of such a vapor separator is disclosed in U.S. Pat. No. 5,368,001.
Typically, pressurized fuel must be returned to the vapor separator because excess fuel is supplied by the fuel pump to ensure an adequate supply and fuel pressure at each fuel injector. In addition to pressurized fuel not used by the fuel injectors, unburned liquid fuel, fuel vapor and air from the engine are also returned to the separator. For example, in two-stroke marine engine applications, fuel collected in an unburned fuel collection system, called a puddle drain system, is periodically purged from the engine into the vapor separator to prevent the engine from running rich and thereby reducing its fuel economy and undesirably increasing exhaust gas emissions.
Unfortunately, fuel is often returned to the reservoir under high pressure as well as high velocity causing the returned fuel to undesirably foam in the reservoir. Additionally, air and fuel vapor being returned to the reservoir can stir up the pool of liquid fuel also causing fuel to foam and vaporize. Fuel foaming is highly undesirable because it can interfere with maintaining enough liquid fuel in the vapor separator for adequate high pressure fuel pump operation. Should the amount of foam in the reservoir become excessive, foam may be pumped to the engine resulting in lean engine operation, stalling or, even worse, overheating of the engine due to fuel starvation.
To reduce fuel foaming, a flat baffle constructed of solid sheet material has been used in the past as a barrier to prevent any stream of returned fuel, vapor and/or air from impinging against the liquid fuel in the vapor separator. Unfortunately, returned fuel often foams as it impinges against the solid baffle and this foam drops below into the pool of liquid fuel because of a gap between the outer edge of the baffle and the sidewall of the vapor separator. Additionally, fuel vapor and air returned to the vapor separator can pass through this gap around the baffle and churn up the liquid fuel, also causing foaming, while undesirably increasing fuel vaporization.
Too much fuel vapor in the separator is also undesirable because it can result in a great deal of fuel vapor being uncontrollably vented from the separator into the intake manifold of the engine, thereby resulting in rough engine operation, spark plug fouling, and increased exhaust gas emissions. Moreover, for two-stroke engines at wide open throttle (WOT) engine operating conditions, the puddle drain system can return a large amount of air to the vapor separator, pressurizing the separator and forcing an excess amount of fuel vapor to vent from the separator into the intake manifold, further compounding these problems.
Complicated mechanisms have been developed in response to these problems. To help control or at least reduce the amount of fuel vapor venting from the separator back into the engine, there usually is a check valve in the vent between the vapor separator and engine intake manifold. To better control and typically reduce the amount of air under high velocity returned by the puddle drain system, a complex mechanical valving system cooperates with the throttle so it opens periodically at idle and low speed engine operating conditions to return fuel and vapor and remains closed at WOT to prevent overpressurizing the vapor separator helping to ensure smoother engine operation.
Unfortunately, these mechanisms contribute additional cost to constructing each fuel handling system because of the additional components and extra assembly required. During manufacturing, this added complexity also can increase the number of fuel handling systems that are rejected during quality control inspection, requiring them to be expensively refurbished or scrapped. Just as bad, mechanisms of this complexity can become dirty, sticky or otherwise inoperable over time, reducing their effectiveness or even adversely affecting engine operation, requiring servicing. Finally, all of these mechanisms do not always suitably retard or prevent fuel foaming and excessive fuel vaporization.